Differences In Litter Characteristics Among The Invasive Plant Xanthium Strumarium And Phylogenetically Related Native Plants Grown Under Different CO₂ Concentrations

Exotic species invasions have caused dramatic impacts on structure and functioning of invaded ecosystems,and exerting tremendous economic loss for society.The effect of global change on invasions of introduced plant species is one of the hotspot in invasion ecology,and CO2 elevation is one of the most global changes.Elevated atmospheric CO2 could affect the decomposition processes and soil resource availabilities through altered the quantity and quality of litter for plants,thus influencing the growth and reproduction of plants.However,the effects of elevated C02 on the properties,allelopathic effects,and decomposition rates of litter of invasive plants are unclear.This study compared differences in litter characteristics,allelopathic effects,and decomposition rates among the invasive plant Xanthium strumarium L.and two phylogenetic native plants(X.sibiricum Patrin ex Widder and Bidens biternata(Lour.)Merr.et Sherff)grown under different CO2 concentrations.Results show that invasive X.strumarium has lower leaf litter nitrogen(N),Hemicellulose,and Lignin concentrations,and higher Cellulose concentration than these two native plants grown under doubled CO2 concentration,but there are no differences in N,Hemicellulose,cellulose,and Lignin concentrations among X.strumarium and these two natives(lower Hemicellulose in B.biternata than the invasives).X.strumarium has higher leaf litter ratio of carbon to nitrogen(C:N)grown under both CO2 concentrations than these two natives.X.strumarium has higher leaf litter carbon concentration(C)than the X.sibiricum and lower C than the B.biternata grown under both CO2 concentrations.Muti-factor analysis of variance(MANOVA)show that the interaction of CO2 concentrations and planting seasons affected the differences of C.N,and Hemicellulose,which indicate that planting season affect the differences of C,N,and Hemicellulose with different CO2 concentrations.MANOVA show that species not affected the differences of Cellulose,Hemicellulose,and Lignin concentrations in root litters.However,there are no differences in C and C:N among X.strumarium and these two natives grown under ambient CO2 concentration,but X.strumarium have lower C than these two natives and has higher C:N than X.sibiricum,and has no difference with B.biternata.There are no differences in inhibiting effects of leaf litter leachates of X.strumarium,X.sibiricum,and B.biternata grown between ambient and doubled CO2 concentrations on seed(X.strumarium,X.sibiricum,B.biternata and Raphanus sativus)germinations.There are larger allelopathic effects of leaf litter leachates of X.strumarium,X.sibiricuum,and B.biternata grown under both CO2 concentrations on X.strumarium,X.sibiricum,B.biternata seeds than R.sativus seeds.Under both CO2 concentrations,all leaf litter leachates have allelopathic effects on the germinations of these four species seeds,and the effects increased with the increasing concentrations of leaf litter leachates.There are no differences in decomposition rates of root litters among invasive X.strumarium and these two native plants,and the differences are not affected by CO2 concentrations and planting seasons.There are no differences in decomposition rates of leaf litter between X.strumarium and X.sibiricum,and these two species are lower than B.biternata.Elevated CO2 concentrations not affected the leaf litter decomposition rates of X.strumarium and X.sibiricum,but the leaf litter decomposition rates of B.biternata increased with the increasing CO2 concentrations,which indicate that the effects of CO2 concentrations on leaf litter decomposition rates are species specific.Decomposition abilities of soils grown X.strumarium and B.biternata are not affected by CO2 concentrations,but elevated CO2 concentrations increase the decomposition abilities of soils grown X.sibiricum,which indicate that the effects of CO2 concentrations on the decomposition abilities of soils are affected by the grown plant species.